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3rd baby 'analysis'

post #1 of 26
Thread Starter 

My midwife made the statement at my appointment last month that it was 'highly unlikely I would have a boy after having two girls.'  At first I didn't think much of it because I've always felt like this one was probably a girl.  However, I started thinking about it and wondering if this was actually true.  I started thinking of everyone I knew with three kids (or more) and made a list.  Then I made a list of which ones had same sex children with the first two.  Here is my analysis and I would be curious what yours is!  :)


2 girls then a boy  =  60% (of my friends)

2 boys then a girl  =  33% (of my friends)

post #2 of 26

DDC crashing- interested to see the answer to this as well.

post #3 of 26







post #4 of 26

Girl, Girl, Girl, this time a Girl too. However my third girl was adopted but the other three are girls

Editted to add that my friend had a girl, boy, boy, boy

post #5 of 26

Me: Boy, girl, girl (current baby in belly is a girl by my feelings)

Sister: Boy, girl, boy

Friend J: Girl, girl, boy

Friend A: Boy, boy, girl, boy, boy

Friend A: Boy, girl, boy

Friend A: Boy, girl, girl

Friend C: Boy, girl, boy

Friend L: Boy, girl, boy


I'd say the odds are more in your favor to have a boy than a girl.

post #6 of 26

Technically, you chances are 50% either way each time no matter what you have had before. But my sister's doc told her after she had a girl and then a boy that once she had a boy she wouldn't have another girl and since then she went on to have 4 more boys! For me its girl, boy, boy and I don't know what this one is yet.

post #7 of 26

I have 2 friends who both had 2 girls and then a boy. shrug.gif  I wonder what the logic or science is behind this... hmmm  I always thought it had more to do when you conceived - like this time around we had intercourse and then almost 2 days later I ovulated.  Everything I read says it will be a boy because the boy swimmers are fast and were probably sitting there waiting for the egg when it dropped.

post #8 of 26
Originally Posted by tracymom1 View Post
 I wonder what the logic or science is behind this

I was wondering as well. Is it same mom/same dad or is it solely on either the mom or the dad but not both? It seems coo coo bananas to me! 

post #9 of 26

Me: Twin girls, girl, girl, boy, boy, girl, boy, girl, boy. It amazes me that our last 5 went boy, girl, boy, girl, boy.

Friend E: boy, boy, girl, girl, girl, boy, girl, girl, boy, boy, boy

Friend K: girl, girl, girl, girl, girl, girl

Friend S: boy, boy, girl, girl, boy, girl

Friend D: boy, boy, girl, girl, girl, girl, boy, girl, girl, boy

Friend AM: girl, boy, girl, boy, boy, boy

Friend M: girl, boy, boy, girl, girl, girl




post #10 of 26

In my Statistics class we actually figured out what the odds were of a couple having a boy after having 2 girls. I think that it was something like 70% chance of a boy and 30% chance of another girl. I'm going to have to look up my notes from Stats a year ago and see what they said. It was really interesting! I think I'll have to email that professor and let him know that I am really using something I learned in his class!


As for my babies, the only boy I have is the one that was conceived when I was having LOTS of sex, like 3 or 4 times a day for over a month. No wonder I got pregnant the second I missed a BCP! My girls were conceived when I was having way less sex, like a couple of times a month for my daughter and twice in one month, a week before ovulation, with my birthdaughter. With this baby the timing is almost identical to my last baby so that's part of the reason that I'm thinking/feeling girl.

post #11 of 26
Thread Starter 

I'm not sure what my midwife's logic was behind other than rumors or her own experience.  I have been amazed at how many friends have so many of the same sex.  I have a friend who has five and four are boys.  I know that Shettles thinks it is when you conceive, but the last two times I conceived on the day I ovulated (was temping) and I had a girl last time and I feel like this one is a girl.  I'm beginning to go more with the theory of acidity levels in your body and how they react to dh's sperm.  I am acidic even though with my first I wasn't vegetarian, but quite the opposite.  Since then I am vegetarian and eat totally and completely differently.  My mom is naturally acidic as she even reacts with any sort of metal that she wears...her skin turns black if she wears a metal watch, earrings, necklace, etc.  Mine does sometimes, too. 


I agree that your odds are generally 50/50 no matter what, but I do think some people are more 'prone' to having one sex or the other.


Here's my breakdown:


GM:  girl, girl, girl

GM:  girl, girl, boy

Aunt: girl, girl, boy

Aunt2:  boy, boy, boy

Aunt3:  boy, boy, girl

Friend N: boy, boy, boy, girl, boy

Friend L:  girl, girl, boy (although skewed b/c they are triplets)

Friend A:  boy, boy, boy

Friend S:  boy, boy, boy

Friend C:  girl, girl, girl

Friend A:  girl, girl, boy

Friend J:  boy, boy, girl

post #12 of 26

I wonder if I'm naturally acidic too. I react to metals too, but part of that is due to allergies.


Okay, I found the statistical breakdown of the odds of a 3rd child being a boy after 2 girls. There is a 3 in 8 chance of having a 2 girls and one boy out of 3 pregnancies which equates to a 37.5% chance, so I was backwards in my PP.



Here's what it looks like in a tree diagram:


ggb statistical odds.jpg

This was one of my favorite things that we learned in Stats because I can use it a lot!  I think I need to do a tree diagram for myself to see what my odds are of a boy vs a girl. :)

post #13 of 26
Thread Starter 

Those are very similar to the statics found on ingender.com.  The ones on there, though, are from a specific study, not a long-term one, however, they say your odds go from a 'normal' 51% chance of having a boy to a 46% chance after two girls. 

post #14 of 26

Yeah, I read baout the Shettles method and really thought it was a boy.  But I also read that as Dad's age they have a better chance of a boy too.  So combining the time(and method) of conception as well as DH is now 41 not 20 like before I figured boy.  Nope, another girl!  Either way I am just happy it is healthy and still shocked/grateful I am even preg. *LOL*

post #15 of 26
We have two boys and just found out we're having another one...so factor me into the three in a row crowd. :-)

We weren't trying to get pregnant AT ALL, but thanks to charting i know that we dtd a whole 4 days before i ovulated, which would be girl timing according to shettles i think...but we seem to be all about boys! Ha!

I recently read that after two of the same sex, the chances of another of the same do go up a bit, but that with the fourth, your chances go back to the average? Something like that. I won't be testing it out, that's for sure. Three is plenty for me. innocent.gif
post #16 of 26
Thread Starter 

This is from ingender.com:


The 51/49 Boy/Girl Ratio

The ratio of 51% boys to 49% girls seen here is representative of overall US birth rates. There are many hypotheses about why there are slightly more boys born each year than girls, but no one knows for sure why this is so. Here are a couple of the theories:

  • Males are more fragile (male infants are less likely to survive their first year, and a man's expected lifespan is less than a woman's). The slightly higher conception rate of males is nature's way of evening out the balance.
  • As Shettles contents, Y-bearing male-producing sperm may have a speed advantage over X-bearing female-producing sperm, more often winning the race to fertilize the egg and resulting in more male conceptions.

Regardless of the reason, the 51/49 ratio remains constant year to year throughout the US population.


Odds of Having a Girl

The odds of having a girl seem decrease after having each boy, but only very slightly. Even after 3 boys, you are only 6.4% more likely to have a 4th boy than a girl.


Previous Children % Girl Births
None dotPink.gifdotBlue.gif 49% Girls
1 Boy dotPink.gifdotBlue.gif 50% Girls
2 Boys dotPink.gifdotBlue.gif 47.7% Girls
3 Boys dotPink.gifdotBlue.gif 43.6% Girls

Odds of Having a Boy

The odds of having a boy seem to increase after having girls, except after 2 girls, when a 3rd girl is more likely.


Previous Children % Boy Births
None dotPink.gifdotBlue.gif 51% Boys
1 Girl dotPink.gifdotBlue.gif 54.5% Boys
2 Girls dotPink.gifdotBlue.gif 46.0% Boys
3 Girls dotPink.gifdotBlue.gif 52.7% Boys

Gender and Birth Order

Given the charts above, it looks like you are slightly more likely to have a boy, regardless of previous children. This is probably due to the overall 51/49 boy/girl birth ratio. This ratio, interestingly, varies slightly with birth order; it isn't consistent among first-borns, second-borns, etc.

1st Born dotPink.gifdotBlue.gif 51.0% Boys
2nd Born dotPink.gifdotBlue.gif 52.2% Boys
3rd Born dotPink.gifdotBlue.gif 48.6% Boys
4th Born dotPink.gifdotBlue.gif 50.8% Boys

Odds of Having an All Same-Gender Family

If there are roughly even odds of having a boy or a girl with each baby, given the laws of chance we should still expect to see some all same-gender families, even in large families. Here is the number of all same-gender families we would expect to see, purely by chance:

Family Size Same-Gender Mixed-Gender
2 Children 50% 50%
3 Children 25% 75%
4 Children 12.5% 87.5%
5 Children 6% 94%
6 Children 3% 97%
7 Children 1.6% 98.4%
post #17 of 26

Your statistics professor needs to talk to a biology professor I think. That analysis is totally wrong biologically.


That ingender info was interesting. IME it seems fairly accurate.

post #18 of 26
Originally Posted by jshannyn519 View Post

Okay, I found the statistical breakdown of the odds of a 3rd child being a boy after 2 girls. There is a 3 in 8 chance of having a 2 girls and one boy out of 3 pregnancies which equates to a 37.5% chance, so I was backwards in my PP.


This would be the total odds of having two girls and one boy, not the odds of having a boy after two girls.  There are 8 total outcomes for having 3 kids, 3 of which leave you with 2 girls and a boy.  Hence, 37.5% chance of 2 girls and a boy.  Those odds also don't take order into account, so you have GGB, GBG and BGG as possibilities for "2 girls and 1 boy".  The odds of GGB is only 1/8, but again that's the odds of the specific order starting from 0 kids.  Sex is generally assumed to be independent of previous pregnancies, so it's built into the tree diagram that for every pregnancy the odds of a boy vs. girl is still the same at 1/2.  What the tree diagram basically says is that the odds "reset" for every baby, and so no matter what the sex of your previous babies you still have a 50/50 shot of having a boy (or a girl).  It's basically treated the same as a coin toss - even if you toss the coin 1000 times and get heads every time, the odds of the next toss being tails are still only 50%.


Sorry if I got a little pedantic there, I taught Statistics as a grad student for a few semesters. 

post #19 of 26

I have heard the old saw about this too -- about boys, e.g. "if you have two boys you have an 80% chance of having a third boy."  And from OBs at that!  They ought to know better. It's all a load of crap.  We may very well be having another boy (we'll find out Tuesday) but I think the ingender stats are probably the closest to the truth of what chances are statistically.  Of course acidity or whatever could be responsible in individual cases.


I think people like to say things like this to be jerks, honestly.  It goes along with the whole prejudice against same-sex families that frankly grates on my last nerve.  All children are a blessing, and each child is a unique human being regardless of what is between the legs.

post #20 of 26

Well said, msmiranda!!


Statistics makes my brain hurt.  It was one of the few classes that I just 'got by' with doing the minimum.  Blech.  Would rather take O Chem again.

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